On account of the lower materials costs, the improved welding properties and ultrasound testing properties and on account of the more favorable fracture mechanics properties, rotors for use at high temperatures in gas or steam turbines are preferably made of ferritic steels. However, the mechanical properties of ferritic steels deteriorate so greatly above 450° C. that it becomes necessary to use austenitic steels.
The rotor, which in gas turbines is located below the hot-gas duct, has long being shielded by separate blades and heat shields made of high-temperature materials. However, this shielding has a highly segmented structure, and the individual elements are only secured to the rotor by various types of hooks. If a ferritic material is used for the rotor, relatively large quantities of cooling air at most 450° C. are required to purge the spaces between the rotor and the shielding elements.
Compressors, even if they have outlet temperatures of more than approximately 450° C., have hitherto generally been designed without any shielding and cooling, since shielding alone provides only a little protection against excessively high peak loads, while cooling with recycling of cooling air into the compressor duct has an adverse effect on efficiency.
Nevertheless, the use of heat shields to shield the rotor from the hot-gas duct has also been proposed for compressors (cf. U.S. Pat. Nos. 5,842,831 and 6,416,276B1). In the case of these known shields, the heat shields are secured to the rotor in a positively locking manner. They therefore have the same drawbacks as those which have already been cited above in connection with the gas turbines with a segmented shielding arrangement.